Research is in progress to: (1) develop an ultrasonic device to assess early formation of periosteal callus and the strength of bony union of surgically produced fractures of canine ulna, and (2) to study comparative healing rates of fractures of the rabbit tibia stabilized with metallic and polymeric intramedullary rods. Pulsed 1/2 mHz ultrasonic signals are transmitted along a segment of bone, including the fracture defect, and the signal wave form components are analyzed for amplitude and transit time. Components have been identified which are indicative of callus formation and cortical bony union. Four materials (316LVM stainless steel, Titanium 6A1,4V, acetal homopolymer "Delrin" and Nylon 101) are being used for internal fracture fixation, and a correlation between torsional strength of the tibia and the material used being studied as a function of healing time. BIBLIOGRAPHIC REFERENCES: Brown, S.A., Mayor, M.B.: Ultrasonic assessment of early fracture callus formation. Biomedical Engineering, 11:124-127, 136 (1976). Brown, S.A., Mayor, M.B.: Early evaluation of fracture healing with ultrasound. Proceedings 28th ACEMB:447, 1975 (Abstract).